This invention relates to a television system for providing a high resolution display frame which can be moved about and freely selected from an array of contiguous frames corresponding to a much larger scene which is transmitted by a separate video signal for each frame and separately recorded on a storage medium. More particularly, the present invention employs television techniques to reproduce visuals with virtually unlimited resolution without requiring that the apparatus forming a television system have a corresponding resolution capability.
The human eye has a sensitivity which will enable one to identify and distinguish a great amount of fine detail within a scene. When a scene consisting of a checkerboard pattern made up of alternating black and white squares is reproduced by a television system, the horizontal scan lines forming the video signal must have a bandwidth consistent with the rate at which the squares change from black to white in each horizontal scan line. It, therefore, follows that as the size of the square in the scene decreases, the frequency video signal increases which, in turn, increases the bandwidth requirement. Television standards in the United States provide for a video signal ranging from 30 cycles per second to about 4 megahertz which gives sufficient picture resolution to enable the viewing of a dot that is subjectively as wide as the spacing between lines. The actual size of the horizontal line depends on the focus, screen size and adjustments of the set but the standards of the system provide that there are always 525 scan lines in a full frame, of which, approximately 480 may be visible in a display.
The television system providing a display of high resolution visuals above that obtainable with a standard television system presents three problem areas. First, there is a practical limit to the resolution obtainable with a television camera which at present has an upper limit of about 1000 lines per raster. This limit is imposed by the size of an electron beam produced in a camera with reasonable sensitivity and at a reasonable cost. Second, the resolution of display monitors are limited in a similar way by the size of the electron beam. The third problem area is the bandwidth requirement which affects the camera circuits, monitor circuits, but more seriously affects connecting links, intermediate recording equipment as well as transmitters and receivers. The bandwidth requirements can be alleviated if the time period for each frame of the picture is increased but then the display has an objectionable flicker. The impact of the flicker can be alleviated by longer storage times by the phosphor screen but even then the resolution obtainable by the display tube is limited to about 1000 lines per frame. The bandwidth required to transmit a picture of 1000 lines per frame is four times that required to transmit a picture of 500 lines per frame. Thus, to convey a 1050-line picture with the same bandwidth requirements as a 525-line picture, the frame repetition frequency must be reduced by a factor of 4.
The use of television techniques in a system for the display of high resolution visuals has been the aim of display engineers for many years. The convenience of recording communications and the distribution of information have been largely outweighed by the limited resolution available when standard video recorders and displays are employed. Special-purpose cameras and flying-spot scanners have a resolution which is much greater than the resolution of conventional recorders and monitors. By taking advantage of the fact that the human eye can only resolve detail in a small area at one time, the television system of the present invention makes available to the eye a conventional television display which can be adjusted to present any desired area of a much larger display forming a scene. The television system of the present invention is effective in a somewhat analogous manner to viewing a scene such as a picture containing very fine detail through a magnifying glass by moving it about the entire scene.